Use of a mixture of carbon dioxide and nitrogen as an inerting and flow medium in powder injection systems for pulverized coal gasification under pressure

ABSTRACT

A powder injection system for use in pulverized coal gasification under pressure is provided. The powder injection system includes a reservoir for stocking the pulverized coal, a plurality of power injection tubes and a metering unit. A mixture of nitrogen and carbon dioxide is fed to the components that are at operating pressure, namely the powder injection tube and the metering unit, as the inerting and flow medium or fluidizing medium. The nitrogen and carbon dioxide mixture-carrying components are heated in such a manner that the temperature is above the threshold of the diphase range. A method is also provided. The method allows reduction of the nitrogen content in the product gas, which nitrogen is caused by the powder injection system, especially when used in pulverized coal gasification under pressure to produce a synthesis gas for the production of different hydrocarbons.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2008/054713, filed Apr. 18, 2008 and claims the benefitthereof. The International Application claims the benefits of Germanapplication No. 10 2007 020 332.4 DE filed Apr. 30, 2007, both of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The subject matter of the application relates to a method for operatinga powder injection system for pulverized coal gasification underpressure and to an arrangement for powder injection for pulverized coalgasification under pressure with the features of the claims.

BACKGROUND OF INVENTION

Nitrogen from the air separation unit is usually used as an inerting andflow medium in pneumatically-operated powder injection systems ofinstallations for pulverized coal gasification under pressure. Thismethod variant has proven itself both in injection systems for powderinjection in high-level ovens and also for pulverized coal gasificationunder pressure and is largely technically mature. Advantageously in suchsystems the dust is already removed in special filter vessels from theexpansion gas of the powder injection transfer tubes and also from thesurplus gas arising under specific operating conditions in the meteringvessel under increased operating pressures. Although the powderinjection systems based on pneumatic compression flow conveyance operatewith very high loading conditions, the nitrogen injected into thegasification systems exceeds the permitted limits in many cases. Thereason for this is also the increasing process pressure in mostapplications. For pulverized coal gasification under pressure, inparticular with the objective of synthesis gas generation for theproduction of different hydrocarbons, the flow is produced after arestriction of the nitrogen component in the product gas.

SUMMARY OF INVENTION

The problem underlying the subject matter of the application is that ofdeveloping a method or an arrangement of a powder injection system forpulverized coal gasification under pressure such that the nitrogeninjection into the subsequent gasification system and the disadvantagesassociated therewith will be restricted.

The problem is solved by the features of the claims.

Inventively the flow after limitation of the nitrogen component in theproduct gas from the pulverized coal gasification under pressure will betaken into account by using mixtures of carbon dioxide and nitrogen asan inerting and flow medium in the powder injection system. The sectionsof the plant operated with the nitrogen/carbon dioxide mixture areheated up to the point at which a temperature above the boundary to thetwo-phase region is produced. Advantageously the invention makes use ofthe fact that not all components have to be operated with thenitrogen/carbon dioxide mixture, but instead heated-up nitrogen is fedto the reservoir as inerting and dispersal medium—with reduced outlaycompared to carbon dioxide.

In a particular embodiment of the invention the nitrogen N₂/carbondioxide CO₂ mixture ratio is dimensioned according to the highestallowable proportion of nitrogen at the flow control unit to the reactoras a measure of the highest allowable injection of nitrogen into theproduct gas of the gasification system. In this case the requiredheating effort for fault-free operation of the powder injection systemis lowered as the proportion of nitrogen in the mixture increases andthus the partial pressure of the carbon reduces.

Advantageous developments of the subject matter of the application arespecified in the subclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the application is explained in greater detailbelow as an exemplary embodiment in a scope required for understandingthe process which refers to a Figure. The figure shows:

FIG. 1 a basic diagram of an inventive pulverized coal-injection system

DETAILED DESCRIPTION OF INVENTION

A reservoir BK under ambient pressure and able to be heated up forsupply of solid material FS, such as pulverized coal for example, isable to be supplied with heated nitrogen N₂ as an inerting and dispersalmedium. The solid material is able to be fed via a flow device to one ormore powder injection transfer tubes SES which are at a high operatingpressure of for example 40 bar. The powder injection transfer tube isable to be fed a nitrogen N₂/carbon dioxide CO₂ mixture as an inertingand flow medium with a temperature above the boundary to the two-phaseregion at high operating pressure. In the upper area of the powderinjection transfer tube the expansion gas is drained away, expanded viaa multi-stage pressure relief facility mEV to ambient pressure anddedusted in a following filter F at ambient pressure. The solid materialis transferred from the powder injection transfer tubes into themetering vessel DG by gravity flow via a suitably dimensioned downpipe.Between two and four powder injection transfer tubes are used in eachpowder injection system.

The nitrogen N₂/carbon dioxide CO₂ mixture is used as fluidization gas.A partial eddy layer is created by the fluidization gas in the bottompart of the metering vessel. In this process the pulverized coal istransferred from a bulk pulverized coal state into the eddy layer andthereby simultaneously put into the flow state. Since it has beenensured in the previous method steps that the gap volume of the bulkpulverized coal in metering vessel is filled with the nitrogen N₂/carbondioxide CO₂ mixture and the nitrogen N₂/carbon dioxide CO₂ mixture islikewise used for the fluidization, the associated gas at the flowcontrol unit to the reactor consists of this nitrogen N₂/carbon dioxideCO₂ mixture.

The nitrogen N₂/carbon dioxide CO₂ mixture is also used as injectiongas. The injection gas is introduced into the powder flow lines.Injection gas feeds can be necessary to recognize faults of the powderfeed to the reactor quickly enough.

Inventively it is proposed to employ a carbon dioxide-nitrogen mixtureof the same composition in all method sections of the injection systemto be operated at high-pressure, namely the powder injection transfertube and the metering vessel.

To lessen the risks resulting from the incidence of liquid carbondioxide when it is used as an inerting and flow medium in powderinjection systems or to reduce the required heating effort for use ofpure carbon dioxide, the method works with mixtures of the two inert gascomponents carbon dioxide and nitrogen.

Because of the thermodynamic properties of carbon dioxide however, a fewspecial characteristics are to be noted in such cases. It is to be takeninto account in particular that pure carbon dioxide at the desiredprocess pressures of above 40 bar already reaches the boundary to thetwo-phase region at ambient temperature. To avoid this, in all processsections which will be operated at or above the required processpressures with carbon dioxide, sufficiently high operating temperaturesare always to be guaranteed.

The mixing of the two inerting and flow media is created in a suitablemanner and provided for use in the powder injection system. The problemsresulting from the use of carbon dioxide as an inerting and flow gas orthe heating effort required for the fault-free operation of the powderinjection system will be reduced as the proportion of nitrogen in themixture increases and thereby the partial pressure of the carbon dioxidedecreases.

The permitted proportion of nitrogen in the mixture is produced from thealready acceptable nitrogen injection into the product gas of thegasification system.

Typical mixture ratios of carbon dioxide/nitrogen are 75/25, 60/40,50/50, 40/60 or 25/75.

The carbon dioxide/nitrogen mixture is already received at the plantboundary with a sufficiently high temperature. The cooling-down of thegas during its application, forwarding and also the method-specific useitself is to be counteracted by a suitable heating system.

It is of particular importance to keep the temperature of the pulverizedcoal created in the upstream dryer mill system at a sufficient highlevel right through to the flow control unit FLE in the reactor. Forthis reason the pulverized coal reservoir operating at ambient pressureand with nitrogen also applied to it as an inerting and dispersal mediumis also heated Likewise the supplied nitrogen is heated up in order toavoid powder cooling e.g. during long plant shutdowns. Inventively anend-to-end heating in the gas storage, forwarding and metering processsections themselves is provided.

To exclude problems from reduced life time of filter elements throughincidence of liquid carbon dioxide as a result of polytropiccooling-down of the medium during transfer tube expansion, the dedustingof the expansion gas under increased operating pressure is dispensedwith.

The pressure of the slightly powder-laden expansion gas is relieved viamulti-stage expansion facilities mEV. The dedusting of the expansion gasis subsequently undertaken in a filter F operating at ambient pressure.

The pipe section between powder injection transfer tube and pressurerelief facility is heated, to compensate for the polytropic expansioncold and maintain the permitted operating conditions of the expansionfilter.

The pressure relief facility is embodied so that the expansion noisesare reduced at the same time. So-called silencer plates known inspecialist circles are used as a pressure relief facility for example.These bring about a reduction of the expansion noises on the one hand bymulti-stage expansion and on the other hand by dividing the hole crosssection required into a plurality of smaller holes. A wear-protectedcontrol valve with downstream silencer is also able to be used If thesemeasures are not sufficient additional soundproofing measures can beused, such as by means of a sound-deadening sheathing for example.

1.-4. (canceled)
 5. A method for operating a powder injection system fora pulverized coal gasification under pressure, comprising: applying anambient pressure to a reservoir which supplies the pulverized coal;applying a high operating pressure to a plurality of powder injectiontubes and to a metering vessel which heats up the reservoir; feedingheated nitrogen to the reservoir as an inerting and dispersal medium;feeding a nitrogen and carbon dioxide mixture to a powder injectiontransfer tube as an inerting and flow medium; and feeding the nitrogenand carbon dioxide mixture to the metering vessel as a fluidizationmedium.
 6. The method as claimed in claim 5, wherein the suppliednitrogen and carbon dioxide mixture is heated up to a temperature abovea threshold to a two-phase region at a high process pressure in ahigh-pressure region of the powder injection system.
 7. A method asclaimed in claim 5, wherein a nitrogen and carbon dioxide mixture ratiois dimensioned according to a highest permitted proportion of nitrogenat a flow control unit to a reactor in accordance with a highestpermissible injection of nitrogen in a product gas of a gasificationsystem.
 8. The method as claimed in claim 5, wherein the high operatingpressure is 40 bar.
 9. The method as claimed in claim 5, wherein thenitrogen and carbon dioxide mixture is used as an injection gas andintroduced into a plurality of powder flow lines.
 10. The method asclaimed in claim 5, wherein the nitrogen and carbon dioxide mixtureratio is 75/25.
 11. The method as claimed in claim 5, wherein thenitrogen and carbon dioxide mixture ratio is 60/40.
 12. The method asclaimed in claim 5, wherein the nitrogen and carbon dioxide mixtureratio is 50/50.
 13. The method as claimed in claim 5, wherein thenitrogen and carbon dioxide mixture ratio is 40/60.
 14. The method asclaimed in claim 5, wherein the nitrogen and carbon dioxide mixtureratio is 25/75.
 15. An arrangement for a powder injection for pulverizedcoal gasification under pressure, comprising: a reservoir to which anambient pressure is applied, the reservoir supplies the pulverized coal;an injection tube to which a high operating pressure may be applied; ametering vessel to which a high operating pressure may be applied,wherein when the high operating pressure is applied to the meteringvessel, the reservoir is heated up, wherein heated nitrogen is fed tothe reservoir as an inerting and loosening medium, wherein a nitrogenand carbon dioxide mixture is fed to the powder injection transfer tubeas an inerting and flow medium, and wherein the nitrogen and carbondioxide mixture is fed to the metering vessel as a fluidization medium.16. The arrangement as claimed in claim 15, wherein the suppliednitrogen and carbon dioxide mixture is heated up to a temperature abovea threshold to a two-phase region at a high process pressure in ahigh-pressure region of the powder injection system.
 17. The arrangementas claimed in claim 15, wherein a nitrogen and carbon dioxide mixtureratio is dimensioned according to a highest permitted proportion ofnitrogen at a flow control unit to a reactor in accordance with ahighest permissible injection of nitrogen in a product gas of agasification system.
 18. The arrangement as claimed in claim 15, whereinthe high operating pressure is 40 bar.
 19. The arrangement as claimed inclaim 15, wherein the nitrogen and carbon dioxide mixture is used as aninjection gas and introduced into a plurality of powder flow lines. 20.The arrangement as claimed in claim 15, wherein the nitrogen and carbondioxide mixture ratio is 75/25.
 21. The arrangement as claimed in claim15, wherein the nitrogen and carbon dioxide mixture ratio is 60/40. 22.The arrangement as claimed in claim 15, wherein the nitrogen and carbondioxide mixture ratio is 50/50.
 23. The arrangement as claimed in claim15, wherein the nitrogen and carbon dioxide mixture ratio is 40/60. 24.The arrangement as claimed in claim 15, wherein the nitrogen and carbondioxide mixture ratio is 25/75.